Background/Purpose: B cells have been implicated in the development of rheumatoid arthritis (RA) based on their production of autoantibodies and cytokines as well as the therapeutic response to B cell depletion therapy. The maturation of B cells occurs in the germinal center and is influenced by multiple factors including T cell dependent CD40-CD40L signals, toll-like receptor signals and cytokines including BAFF and IL-21. Each of these is a potential therapeutic target in RA. In this study we examined the response to IL-21 as measured by phosphorylation of STAT3 (pSTAT3), to better understand its potential role in RA.

Methods: We utilized frozen PBMC from a cohort of RA subjects and healthy controls obtained from the BRI Rheumatic disease Registry. Samples were thawed, rested for 1 hour and were stimulated with cytokine; IL-21 (50 ng/mL and 15 pg/mL) for 15 and 45 minutes (n=20 per group); IL-10 for 10 min at 10 ng/mL (n=20 per group); or IL-4 at 100 ng/mL for 15 min (RA n=10, Control n=12).  Response to IL-21 and IL-10 was measured as mean fold change in phosphorylation of STAT3 (pSTAT3) and for IL-4 pSTAT6. IL-21R, the common gamma chain and total STAT3 expression were determined through flow cytometric analysis.

Results: We determined that RA subjects exhibit enhanced IL-21 signaling in total B cells (p = 0.02), memory B cells (p = 0.0096), IgM+ memory B cells (0.01), naïve B cells (p = 0.02) and transitional B cells (0.005) but not in the more mature switched memory B cells as compared to controls. We observed no significant differences in IL-10 or IL-4 stimulations. Further, IL-21 signaling in total B cells of RA subjects as measured by pSTAT3 positively correlated with the expression of IL-21R (p = 0.0004, r = 0.70). Similarly we found a significant correlation with the common gamma chain level of expression (p = 0.01, r = 0.55). When we measured total STAT3 we observed no significant differences between RA and control subjects.

Conclusion: We found that the response to IL-21 is enhanced in the B cells of subjects with RA in comparison to healthy age and gender matched controls.  This is unique to IL-21 and not other cytokines; IL-4 which signal through the common gamma chain nor IL-10 which signaling via STAT3, suggesting a link with the IL-21R specifically. Consistent with this we found an increase in the expression of the IL-21R on the cell surface. This heightened response has the potential to enhance or alter the maturation of B cells leading to alterations in antibody and cytokine production in RA. Characterizing the response to IL-21 in RA B cells is important as it relates to disease pathogenesis but also is vital as therapeutics that target this cytokine and its signaling pathway are currently under development. Thus this work may have implications with respect to how best to use such drugs in the setting of RA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-il-21-signaling-pathway-is-enhanced-in-ra-b-cells-and-has-the-potential-to-alter-development-and-cytokine-production-in-ra-b-cells/